Detailing

To add details to my model, I used ZBrush's Spotlight tool. I overlapped my reference image on my model (Fig.10), and I projected the details, but only on the geometry - I dealt with the colors later (Fig.11).

Fig.10

Fig.11

The next step was to remove all the unwanted details, such as the glasses, and manually refine the skin (Fig.12).

Fig.12

Texturing

Once the detailing was complete, I opened up the reference photo in Photoshop, and I removed all the visible details, in order to achieve a "diffuse-only" type of image (Fig.13).

Fig.13

Then I went back to ZBrush again and used Spotlight to project only the color information this time over my model (Fig.14).

Fig.14

I did the same process using various photos to cover the entire head (Fig.15), and then I generated the texture from the Polypaint (Fig.16).